The present invention relates to spectrophotometric or densitometer apparatus, and in particular to such apparatus that is portable, easily calibrated, and in which the detection of radiation transmitted from the specimen is enhanced by an electronic bridge sensor.
Spectrophotometric apparatus generally utilize absorption filter devices to select and detect the necessary information to identify the elements or components of a given specimen. Selective absorption is generally achieved with the use of color filters, interference filters, echelon gratings or prisms. In particular, the information obtained from spectrophotometric instruments is produced by passing a light beam, such as is obtained from a monochromatic light source, or simply by means of colored filters, through suitably placed glass transparent recipients in the path of the light beam. The loss of the light by absorption, for example in the specimen or object, is then interpreted in terms of the resultant optical density or induction of the chemical composition of the specimen, or a combination of both optical density and chemical techniques.
Alternatively, the spectrophotometric information or data is obtained by reflecting radiation from a suitable broad band or a narrow band light emitting source, such as a monochromatic light source, or the use of colored filters, interference filters, echelon gratings, or prisms, etc., and collecting the light reflected from a specimen or object by a suitable photosensor, such as a photomultiplier or light sensitive receiver of the solid state type that are well known to those skilled in the art to which the invention is directed. The necessary absorption filters, or narrow band radiation-producing elements are then inserted in the reflected light path between the specimen and the photosensitive device.
The specimen or object may be illuminated with a wide band light source, such as a projection lamp with a color temperature of over 3000 degrees fahrenheit, or a Xenon high pressure arc lamp, with an absorption filter in front of the photoelectric sensor or receiver. Alternatively, a dispersive element such as a grating may be placed in front of the photosensitive device, thereby selecting the precise wavelength at which the absorption occurs.
The advantages of such a technique over the classical photometer, spectrophotometer or colorimeter, is simply that the specimen or object to be examined is irradiated with a higher intensity irradiation than if the light radiation were, for example, monochromatic by the placement or insertion of the filters between the light source and the specimen as opposed to the insertion of the absorption filter between the reflected light rays from the object and the photosensitive element or receiver. However, such techniques have not been completely successful in enhancing and increasing the sensitivity of the photosensitive response of the light radiation detection apparatus, thereby presenting a need for improvement in the latter mentioned apparatus.